Question

how to find refractive index of aliquid using plane mirror and convex lens

Answer 1

by using formula
Refractive index/the speed of light in a specific medium.

Answer 2

Let $f_1$ is the focal length of glass convex lens and $f_2$ be the focal length of liquid lens. The focal length of the combination of two lenses can be taken as F.

Then,

$\frac 1F= \frac 1f_1+\frac 1f_2$

$\frac1f_2= \frac1F-\frac1f_1$  

The liquid lens formed is a planoconcave lens.  

According to lens maker’s formula

$\frac1f_2= (n-1) [\frac1R_1-\frac1R_2]$

Since the liquid lens is planoconcave, $R_1$ = R and $R_2$=  ∞

So, the equation becomes  

$\frac1f_2=\frac{(n-1)}{R}$

Refractive index n= 1+$\frac Rf_2$